sim-se: small refactor on pipe syscall
sim-se: small refactor on pipe syscall

Change-Id: I02ffb1c4af980554ff12ac7d11d32ba80fe261c5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/12308
Reviewed-by: Brandon Potter <0c4047814a967fe28855a3d9d73d9b4959444c57@amd.com>
Maintainer: Brandon Potter <0c4047814a967fe28855a3d9d73d9b4959444c57@amd.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5